1. Field of the Invention
The present invention relates to patient nasal interfaces for gas delivery, gas sampling, and/or combined gas delivery and sampling.
2. Description of the Related Art
Obstructive sleep apnea or OSA, obstructive sleep hypopnea, and upper airway resistance syndrome (UARS) are among a variety of known disorders characterized by episodes of complete or partial upper airway obstruction during a state of diminished consciousness, such as sleep, anesthetization, or post anesthesia. OSA, hypopnea, and UARS cause intermittent interruption of ventilation during sleep with the consequence of potentially severe oxyhemoglobin desaturation. Typically, those afflicted with OSA, hypopnea, and UARS experience repeated, frequent arousals from sleep in response to the oxygen deprivation. The arousals result in sleep fragmentation and poor sleep continuity.
Consequences of OSA, hypopnea, and UARS may include debilitating daytime sleepiness and cognitive dysfunction, systemic hypertension, cardiac dysrhythmias, pulmonary artery hypertension and congestive heart failure. Other consequences may include a predisposition to myocardial infarction, angina pectoris, stroke, right ventricular dysfunction with cor pulmonale, carbon dioxide retention during wakefulness as well as during sleep, and continuous, reduced arterial oxygen tension. Moreover, the cognitive impairment resulting from OSA, hypopnea, and UARS puts those afflicted at elevated risk of accidents.
The pathogenesis of the airway obstruction that characterizes OSA, hypopnea, and UARS can include both anatomic and functional abnormalities of the upper airway that result in increased air flow resistance. Such abnormalities may include narrowing of the upper airway due to suction forces created during inspiration, the effect of gravity pulling the tongue back towards the pharyngeal wall, and insufficient muscle tone in the upper airway dilator muscles, among others. It is also believed that excessive soft tissue in the anterior and lateral neck, as commonly observed in obese persons, can apply sufficient pressure to internal structures to narrow the upper airway and restrict air flow.
Conventional treatment of OSA, hypopnea, and UARS has included surgical intervention, such as uvalopalotopharyngoplasty, gastric surgery for obesity, mandibular advancement procedures, maxillo-facial reconstruction, and tracheostomy. However, surgery potentially involves considerable risk of post-operative morbidity and mortality. In addition, the failure rate of surgery is disturbingly high. Pharmacological therapy has also been proposed to treat OSA, hypopnea, and UARS; however, results have been generally disappointing.
More recently, continuous positive airway pressure (CPAP) or bi-level positive airway pressure applied during sleep has been used to treat OSA, hypopnea, and UARS patients. Positive pressure is applied in the upper airway to splint or support the airway open, thereby preventing its collapse and the resultant airway obstruction. A typical positive airway pressure device comprises a flow generator (e.g., a blower) that delivers gas via a delivery conduit to a patient interface, such as a mask. It is also known to deliver the positive airway pressure therapy as a continuous positive airway pressure (CPAP), a variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle (Bi-PAP), or an auto-titrating pressure that varies with the monitored condition of the patient. Pressure support therapies are also provided to treat other medical and respiratory disorders, such as Cheynes-Stokes respiration, congestive heart failure, and stroke.
Many patient interfaces are well known in the art. For instance, masks which provide a seal between the compressed air and the patient are common. These interfaces include nasal pillows with or without prongs which fit into the nares of the patient, nasal cannulas, nasal masks which fit over the patient's nose, nasal-oral masks that fit over the mouth and nose, and full face masks which fit over the patient's entire face. For such devices to be effective, two competing goals need to be balanced: comfort and functionality. Comfort may be enhanced by reducing the area of contact between the mask and the patient; or use of a soft, lightweight, flexible material. However, taken to an extreme, comfortable masks may prove to not function adequately. On the other hand, if comfort is not taken into account, even mechanically effective patient interfaces may have low patient compliance.
For purposes of description, the discussion herein is focused on patient interfaces and/or cannulas for use with human patients, it being understood that the present invention is not limited in scope only to use with human patients and can beneficially be used in various other contexts. For example, the present invention may also be used in the area of veterinary medicine where the “patients” are animals.
Different types of nasal interfaces are used to deliver gas, such as air or oxygen, to patients who need assistance to breathe properly, as discussed above, and/or to collect expired gas, such as carbon dioxide, from patients to monitor respiration. In some applications, a sidestream of the patient's exhaled breath flows through the interface to a gas analyzer to be analyzed. The results of this non-invasive analysis provide an indication of the patient's condition, such as the state of the patient's pulmonary perfusion, respiratory system, and/or metabolism.
Some nasal interfaces are perceived to not remain in position during use, and as a result are not comfortable to the patient. This may be due, in part, to differences between patients in the spacing between the patient's nostrils, the shape of the patient's nostrils, and/or the spacing between the patient's nose and mouth. It may also be due to differences in airflow from the two nostrils. It is desirable to provide an interface with improved comfort for the patient.
In addition, the nasal resistance between subjects can vary significantly. As such, the nasal airflow can often be quite asymmetric between the two nostrils. This can affect the efficiency of gas delivery, as the delivery will depend upon the nature of an obstruction in one or both nostrils, and how the gas is delivered. Gas that is allowed to escape from the system, i.e., not enter the patient's nostril upon exiting the cannula, decreases the efficiency of the system. A simple means to increase the amount of gas that is inhaled by the subject without wasting the gas is desired.
Many patient interfaces are configured to direct gas either directly into or directly out of the nasal cavity of the patient. While advantageous in some applications, it would be desirable to have a device which allows the gas to be directed into a particular direction to optimize the gas flow.